1. Field of the Invention
The present invention relates to an inhibitor switch for detecting change gear range positions of an automatic transmission.
2. Description of the Related Art
Conventionally, as an inhibitor switch, there has been an inhibitor switch which makes a movable contact rotating along with an axial rotation of a manual valve shaft of an automatic transmission slidably moved relative to a fixed contact mounted on a transmission case side of the above mentioned automatic transmission and detects the changeover of a change gear range of the automatic transmission in response to the position of the movable contact to the fixed contact. With respect to the detection using such a slidable contact, there has been a problem that the contact control of the surface of the contact is extremely difficult and hence, there are so much noise signals that the control with a microcomputer becomes difficult.
To the contrary, an inhibitor switch adopting a non-contacting method can eliminate noise signals derived from the contacting and hence, it is suitable for the control using a microcomputer. As such an inhibitor switch adopting the non-contacting method, there has been an inhibitor switch which provides magnetic sensors at respective change gear positions and detects the changeover of the change gear range based on ON/OFF signals of respective sensors or an inhibitor switch which reduces the number of the magnetic sensors and detects the changeover of the change gear range based on the combination of signals of the magnetic sensors.
As the inhibitor switch which provides magnetic sensors at respective change gear positions, there has been an inhibitor switch shown in FIG. 18 to FIG. 20, which is described in Japanese Utility Model Publication No. 101623/1980, for example. To briefly explain the constitution of the inhibitor switch first of all, a rotary element 105 is mounted on a manual valve shaft 103 of an automatic transmission 101 and a permanent magnet 107 is supported on the rotary element 105. Further, on a housing 109 side of the automatic transmission 101, magnetic sensors 111 which are arranged corresponding to change gear range positions are supported. These magnetic sensors 111 are constituted by lead switches.
Then, when the permanent magnet 107 is moved due to the rotation of the manual valve shaft 103 in response to the changeover of the change gear range, a contact of any one of magnetic sensors 111 which faces this permanent magnet 107 in an opposed manner is closed and any one of the change gear range positions can be detected by reading the resistance values connected to respective magnetic sensors 111 which are different each other.
However, in such a structure, it is necessary to provide the magnetic sensors 111 at respective change gear positions so that the number of magnetic sensors becomes large and there exits a limit with respect to the miniaturization of the inhibitor switch. Accordingly, it has been almost difficult to arrange the inhibitor switch in the inside of a transmission case.
Further, the inhibitor switch having the above mentioned structure has a problem that there exists a limit with respect to an accurate detection. That is, when the manual valve shaft 103 is rotated due to the transmission manipulation and the permanent magnet 107 is moved between respective magnetic sensors 111 in response to this rotation, at an intermediate position between these magnetic sensors 111, a state that the magnetic sensors 111 disposed in front of and behind the magnetic sensor 107 turn OFF or a state that both of such magnetic sensors 111 turn ON may arise. When both of the magnetic sensors 111 turn OFF, it is impossible to detect where the change gear range position of the automatic transmission 101 exists while when both of the magnetic sensors 101 turn ON, it becomes impossible to detect which position the change gear range exists.
Accordingly, in the state that the permanent magnet 107 is disposed in such an intermediate position, when the inhibitor switch suffers from a failure, it has been impossible to detect the change gear range position where the failure occurs so that the detection accuracy is low. Accordingly, the detection having an improved reliability has been requested.
In the inhibitor switch which reduces the number of magnetic sensors and performs the detection based on the combination of signals of the magnetic sensors, by changing the combination of sensor signals at respective change gear range positions, the reliability of the inhibitor switch when the sensor suffers from the failure can be enhanced. That is, in the above-mentioned structure which turns ON/OFF the magnetic sensors 111 of respective change gear ranges, when any one of the magnetic sensors 111 is connected due to a failure such as a short-circuiting or the like, even when a shift lever is manipulated from N (neutral range) to D (drive range), there is a possibility that a signal indicative of P (parking range) is outputted or the like. With use of the above-mentioned combination of signals, such an erroneous outputting can be suppressed.
However, only with the mere combination of several kinds of signals corresponding to the change gear range positions, when any one of the magnetic sensors suffers from the failure, it gives rise to a common combination mode at different change gear range positions and there is a possibility that the correct signals can not be distinguished from error signals. Accordingly, in a usual case, the combination modes are prevented from becoming in common with the use of a combination signal which is added with one bit to the combination signal.
That is, when the combination modes of signals are made in common at different change gear ranges due to the failure and hence, a signal that the change gear range is changed directly from P to N is outputted or the like, it is possible to distinguish the correct signals from error signals by storing conditions that there is no possibility that the change gear range is directly shifted from P to N into the microcomputer. However, at an end portion such as P, even when the shift lever is not manipulated, a signal that the change gear range is shifted from P is outputted and hence, there is a possibility that the accurate signal can not be distinguished from the error signal. Accordingly, in a usual case, the provision is made such that one bit is added to the combination signal so that even when any one of the magnetic sensors suffers from the failure, signals which agree with each other are not generated at respective detection positions. Accordingly, the number of magnetic sensors is increased correspondingly so that it also gives rise to a problem that the inhibitor switch becomes large-sized.
Further, the inhibitor switch also has a problem that the detection accuracy at the intermediate position is low as in the case of the previously-mentioned inhibitor switch.
It is an object of the present invention to provide an inhibitor switch, which can miniaturize the constitution thereof and also can remarkably enhance the detection reliability.
The inhibitor switch according to the present invention has the following characteristics.
(1) The inhibitor switch according to the present invention comprises a permanent magnet and a magnetic sensor which detects a magnetic force of the permanent magnet in a non-contacting state and outputting a linear change in a voltage value in response to a change in a relative position between the permanent magnet and the magnetic sensor, wherein either one of the permanent magnet and the magnetic sensor is mounted on a manual valve shaft side for changing over a change gear range position of the automatic transmission by operating a manual valve of the automatic transmission in an interlocking manner with the manual valve shaft, and the other one of the permanent magnet and the magnetic sensor is mounted on a transmission case side of the automatic transmission, and the change gear range position of the automatic transmission is detectable in response to an output of the voltage value corresponding to the change gear range position.
(2) In the inhibitor switch as set forth in section (1), the permanent magnet is mounted in a ring form on a movable element made of a non-magnetic material which is supported such that it is integrally rotatable with the manual valve shaft, and the magnetic sensor is mounted on a pole base made of a non-magnetic material which is fixedly supported on the transmission case side.
(3) In the inhibitor switch as set forth in section (2), the permanent magnet has a magnetic boundary surface between an S pole and an N pole, and the permanent magnet is arranged relative to the magnetic sensor using the boundary surface as a reference position and the permanent magnet is capable of performing a relative rotation to the magnetic sensor in the directions of both sides of the boundary surface.
(4) In the inhibitor switch as set forth in section (3), a stopper is provided between the pole base and the movable element so as to set the relative rotation of the permanent magnet to the magnetic sensor within a predetermined angle.
(5) In the inhibitor switch as set forth in any one of sections (2) to (4), a lead terminal of the magnetic sensor has a distal end thereof pulled into a recessed portion formed in an outer surface of the pole base and a distal end of a connector terminal for an external connection which is supported on the pole base is pulled into the recessed portion and is electrically connected to the distal end of the lead terminal, and the recessed portion is sealed with resin.
(6) In the inhibitor switch as set forth in any one of sections (2) to (4), the pole base is formed of resin by molding and the magnetic sensor is arranged in the pole base in an embedded form by an insert molding.
(7) In the inhibitor switch as set forth in section (2), a plurality of the magnetic sensors are provided corresponding to the number of magnetic boundary surfaces of the permanent magnet.
In the invention as set forth in section (1), the linear change in the voltage value is outputted in response to the change in the relative position of the permanent magnet and the magnetic sensor corresponding to an axial rotation of the manual valve shaft and the change gear range position of the automatic transmission can be detected by an output of the voltage value corresponding to the change gear range position so that the change gear range position of the automatic transmission can be surely detected due to the change in the voltage value. Further, even in an intermediate state shifting to each change gear range position, the linear change in the voltage value can be outputted so that it becomes possible to accurately detect an interval between change gear range positions in which the permanent magnet or the magnetic sensor is currently being shifted. Due to such a constitution, even when the inhibitor switch suddenly suffers from a failure, the position and the change gear direction of the permanent magnet or the magnetic sensor at the time of the occurrence of the failure can be accurately judged so that the change gear range of the automatic transmission can be properly controlled whereby the reliability of the inhibitor switch can be remarkably enhanced. Further, the number of the magnetic sensor may be reduced to one so that the inhibitor switch can be largely miniaturized as a whole.
In the invention as set forth in section (2), in addition to the advantageous effect of the invention as set forth in section (1), since the permanent magnet is mounted on the movable element made of a non-magnetic material which is supported such that it is integrally rotatable with the manual valve shaft and the magnetic sensor is mounted on the pole base made of a non-magnetic material supported on the transmission case side, the permanent magnet performs the relative rotation thereof to the magnetic sensor in response to the axial rotation of the manual valve shaft so that the linear change in the voltage value can be accurately outputted whereby a further accurate detection can be performed.
In the invention as set forth in section (3), in addition to the advantageous effect of the invention as set forth in section (2), since the permanent magnet has the magnetic boundary surface between the S pole and the N pole, and the permanent magnet is arranged relative to the magnetic sensor using the boundary surface as the reference position and performs the relative rotation to the magnetic sensor in both side directions of the boundary surface, the linear change in the voltage value can be ensured in a wide range so that the change in voltage value at each change gear range position can be easily distinguished whereby a further accurate detection can be performed.
In the invention as set forth in section (4), in addition to the advantageous effect of the invention as set forth in section (3), since the stopper which sets the relative rotation of the permanent magnet to the magnetic sensor within the predetermined angle is provided between the pole base and the movable element, the voltage value can be surely detected within a range of the linear change so that a further accurate detection can be performed.
In the invention as set forth in section (5), in addition to the advantageous effect of the invention as set forth in any one of sections (2) to (4), since the lead terminal of the magnetic sensor has the end portion thereof pulled into the recessed portion formed in the outer surface of the pole base, the distal end of the connector terminal for an external connection supported on the pole base is pulled into the inside of the recessed portion and is electrically connected to the distal end of the lead terminal and the recessed portion is sealed with resin, the magnetic sensor can be mounted on the pole base thereafter so that the freedom of assembly can be increased.
In the invention as set forth in section (6), in addition to the advantageous effect of the invention as set forth in any one of sections (2) to (4), since the pole base is formed with resin by molding and the magnetic sensor is arranged in the inside of the pole base in an embedded form by an insert molding, even when oil or the like intrudes into the inside of the pole base, there is no possibility that the oil or the like comes into contact with the magnetic sensor so that a further accurate detection becomes possible. Further, the accuracy of the assembled position of the magnetic sensor is enhanced so that a further accurate detection is possible.
In the invention as set forth in section (7), in addition to the advantageous effect of the invention as set forth in section (2), since a plurality of magnetic sensors are provided corresponding to the number of the magnetic boundary surfaces of the permanent magnet, the linear changes of the voltage values can be detected by respective magnetic sensors and the change gear range positions can be detected by integrating these voltage values so that a further accurate detection can be performed. Further, even when any one of the magnetic sensors suffers from a failure, the linear change in the voltage value can be accurately outputted with use of other magnetic sensor so that the detection of the change gear position can be continued.